1) Field of the Invention
The present invention relates to a method and apparatus for spinning hollow bicomponent filaments. More particularly, the invention relates to using a spinneret and a shim for hollow bicomponent filament spinning. More particularly still, the spinneret has a plurality of capillaries having asymmetric apertures, and the shim has a plurality of fan shaped openings.
2) Prior Art
Mono-component filaments are well-known and a variety of spinning packs and spinnerets have been employed in the production of hollow filaments. A conventional mono-filament spinning assembly involves feeding polymer through spinneret holes then forcing the polymer through apertures at the bottom of the hole to form a hollow filament. Subsequently, the filament can be mechanically crimped to provide additional bulk.
Spinning packs are also well-known for the production of bicomponent filaments having side/side and sheath/core configurations. A conventional bicomponent spin pack assembly involves feeding molten sheath forming material to spinneret holes, in a direction perpendicular to the holes, and injecting molten core forming material into the sheath forming material as it flows into the spinneret holes.
Traditionally, use of bicomponent polymers to produce hollow filaments has been impeded by kneeing of the filament. For bicomponent hollow filament production, the polymers must first be fed to opposed parts of the spinneret hole and through opposed apertures in a bottom of the spinneret hole. Since the polymers have different melt viscosities (hereinafter MV) there is more resistance to the higher MV in going through its designated aperture than for the lower MV in going through its designated aperture. The difference in MV causes a hydraulic split where the higher MV polymer partially splits to egress the aperture designated for the lower MV polymer. The lower MV polymer, forced to egress a reduced aperture area, exits at a higher velocity causing the filament to xe2x80x9ckneexe2x80x9d, that is veer substantially from a linear direction. Kneeing causes operational problems with the spin pack such as difficulty in extruding the filaments and increased filament breakage.
Accordingly, there is a need for an improved spin pack assembly wherein a hollow bicomponent filament can be produced without excessive kneeing. Additionally, there is a need for an improved shim for directing one polymer to a designated part of the spinneret hole. Further there is a need for improved spinneret openings each having apertures configured in the capillary to eliminate hydraulic split of the polymers. Lastly, there is a need for a self-crimping hollow bicomponent filament.
The present invention is directed towards a spin pack assembly and method for spinning hollow bicomponent filaments which do not knee and are self-crimping. Since each polymer has different properties, and in particular substantially different shrinkage rates, the bicomponent filaments will self-crimp in spiral after being drawn and heated. The spiral crimp bicomponent filaments have substantial bulk suitable for use in fiberfill for sleeping bags, winter quilted clothing and other similar applications requiring a high thermal insulation xe2x80x9cRxe2x80x9d value.
The spin pack assembly forms hollow self-crimping filaments by utilizing a unique shim and a spinneret having openings with asymmetric apertures to separately handle at least two polymer streams. Upon exiting the apertures, the polymer streams join to form self-crimping hollow filaments. The shim is provided with a plurality of openings which direct a first polymer to a first part of the spinneret holes while restricting the first polymer from a remaining part of the holes. Distributor holes offset from the holes in the spinneret, deliver a second polymer to the opposed remaining part of the spinneret holes. The polymers are then forced through separate apertures provided in a lower section of the spinneret holes. The apertures are configured to avoid hydraulic split of the polymers and accordingly avoid kneeing of the resulting hollow bicomponent filament.
In the broadest sense, the present invention also is directed towards a spin pack assembly comprising a distributor having outer flow passages for the flow of a first polymer and an inner polymer flow passage for the flow of a second polymer, and a spinneret secured relative to the distributor and communicating with the distributor to receive the first and second polymers. The spinneret has a top face directed towards the distributor, an opposed bottom face and a plurality of holes extending from the top face to the bottom face. The holes have a lower section which is provided with a plurality of apertures. Each of the apertures communicate with substantially only the inner flow passage or at least one of the outer flow passages.
In the broadest sense, the present invention also is directed towards a spin pack assembly comprising a distributor having outer flow passages for the flow of a first polymer and an inner polymer flow passage for the flow of a second polymer, and a spinneret secured relative to the distributor and communicating with the distributor to receive the first and second polymers. The spinneret has a top face directed towards the distributor, an opposed bottom face and a plurality of holes extending from the top face to the bottom face. The holes have a lower section which is provided with a plurality of apertures in which substantially only one of the first or second polymers egresses any one of the apertures. The first and second polymers flowing through the apertures are capable of forming hollow filaments due to the configuration of the apertures.
An object of the present invention is to configure the spinneret apertures with different cross-sectional areas.
Another object of the present invention is to limit the apertures to two C-shaped apertures.
Still another object of the present invention is to provide a shim secured between the distributor and the spinneret. The shim is provided with a plurality of openings having a first portion and a second portion. The first portion is positioned between a bottom section of the distributor outer flow passages and the spinneret holes to form a continuous path therebetween. The second portion extends from the first portion in a direction away from a first part of the holes to form a continuous course for polymers to flow from the spinneret, through the second portion, to a remaining part of the holes which is opposed to the first part.
A further object of the invention is to configure the first portion in circular shape and the second portion in block-arc shape. Additionally, the first portion is coaxial with the holes, and the second portion spans an arc of about 120 degrees.
A still further object of the present invention is to provide the distributor outer flow passages with a bottom section which is offset from the spinneret holes such that if the bottom sections were extended, the bottom sections would be positioned within the first part of the respective spinneret hole.
In the broadest sense, the present invention is directed towards a method for producing hollow bicomponent filaments. The method includes providing a distributor having a plurality of outer polymer flow passages which have a bottom section, and an inner flow passage. A spinneret, secured relative to the distributor and having a top face directed towards the distributor and an opposed bottom face, is also provided. Holes are provided in the spinneret which extend from the top face to the bottom face. The holes have a first part, a remaining part, and a lower section having a plurality of apertures. The holes are axially offset from the bottom sections such that the bottom sections would be positioned within the first parts if extended. A source for a first polymer and a source for a second polymer are provided. The first polymer is forced through the outer flow passages, through the first part of the holes and through any of the apertures positioned on the first part of the spinneret holes. The second polymer is forced through the inner flow passages, through the remaining part of the holes and through any of the apertures positioned in the remaining part of the spinneret holes. Upon exiting the apertures, the polymers form into filaments which are quenched.